Neutralizing device for vacuum tubes



A. D. RING NEUTRALIZ ING DEVICE FOR VACUUM TUBES I Filed June 5. 1929 t nun.

His Att o 2: 9 /5 rwy f F\- )1? //8 Q 5 2s I! 7 20 E Inventor: Andrew DRmg,

T'neH The; present invention relates to the neu- Patented Aug. 25, 1931 annnnw, i5. Jame,

PATENT? OFFICE wfscnmm YORK, Assrenon'ro GENERAL ELECTRIC COMPANY; a oonroea'rron or NEW'YORK g nnnrimniz'inennvion nor; VACUUM TUBES Application" fi1ed'-June 5', 1929. sem No. 368,704.

tralization of feed b-ackthrough the" interelectrode capacity of a vacuum tube or other electric discharge device", between circuits coupled-by such device, and has foritsobject toprovide an improved neans for neutralizing the effects of such capacity to'preventifeedback, which means is adapted to beapplieddirectly to the tube or device'ot the electric discharge type with'out involv ing long external connections to the circuits coupled thereby. 1 I The means of the present invention is particularly adapted for neutralizing the. capac-' ity coupling between the-plate and grid circuits of a three element vacuum-tube when such circuits employ relatively long leads between the tube and the remaining elements of said circu'its. J Y The invention will be better understood from the following description when con sidered in connection with the accompanying drawing and its scope Willbe pointed out in the appended claims. I Y 1 In the drawing; the figureisja circuit diagram 'of two circuitsc'oupled by a three element vacuum tube, and provided with a neutralizing means embodying my invention. ..-Referring tothe drawing, 5 is an electric discharge deviceof the vacuum tube, three element type, having a cathode 6, ananode 7, and afcontrol electrode or g'rid'S. Between the control grid and the cathode is connected an excitation or input circuit 9"havingsuitable tuning elements such as Ian input'transformer--11 and a tuningcondenser 12 and relatively long circuit leads 13 between the tuning elements of the circuit and the'tube. The input circuit includes, a'suitable bias battery or other source of-bias potential 14: for the control'grid.

- Connectedbet'wen the anodeT'7and'the cathode 6 is an 0u'tputcircuite17 which'is coupled to 'a' tuned; circuit 18, and includes a source of anode potential 19. -This circuit is also provided with relatively long leads '20 between the essential elements of the circuit and the tube. Tuning elements 11 and 12 represent any suitable input impedance .while the coupled circuit 18 represents any suitable output impedance for the tube.

a In an arrangement of this character employing relatively long connecting leadsbetween the input and output impedances and the tube, it is difficult to provide a neutralizing. means for preventing feed back of energy between'the circuits coupled through the inter-electrode capacity of the tube. This is for the reason that with systems heretofore employed an additional connection lead is necessary between the tube and either the input or 'the'output impedance for adjusting one or the other of these impedances to effect neutralization. In accordance with the invention' the input and output impedances may be of any suitable type and located at any desired distance from the tube which servesto couple them, and the neutralizing meansis applied directly to the tube substantially at its terminals. 1

The elements of the neutralizing means are a tapped inductive reactance or transformer 21 and a neutralizing condenser 22 in -series therewith. In practice these elements areembodied in a single instrument or device indicated within the dotted lines, which device is adapted to be connected directly to the ter; minals of the tube. Connection between the tube and the neutralizing device is made between oneend of the transformer winding 21' and the anode 7 through condenser 22. The opposite end of the transformer winding isconnected to the'contr'ol electrode 8. A tab 23 is connected with the cathode. This divides the winding andplaces'a separate section in shunt with each input and output circuit. I 4

To prevent ashort circuit on the bias battery 14, a blocking condenser may be included in circuitwith it and the transformer 21.

In the present example this condenser is placed in the control electrode connection as indicated at 15. It should be understood that this condenser is used only when necessary to block the circuit against direct current flow.

The neutralizing condenser 22 may be of any suitable type having a capacity substantially equal to the inter-electrode or anodegrid capacity of the tube although it is possible to vary this capacity if the transformation ratio in the'transformer' 21 is changed in accordance therewith. The transformer is preferably one continuous inductive reactance winding. butdivided electrically as shown into primary and'secondary sections by the tap connection, and serves the purpose of reversing the phase of the voltage feed back through the neutralizing condenser to the grid of the tube. For this purpose the winding sections or transformer windings thus established are closely coupled magnetically and in addition should possess relatlvely high reactance compared with the input or output reactances' of the tube. Any other suitable arrangement providing magnetically close coupled transformer winding-s in opposing phase relation may be provided however, although the continuous tapped Winding of the present example is at present preferred.

= In the present example, tap 23 is a midtap' in the winding and is grounded or connected to thecatliode circuit, thus providing a common connection for both windings established by the tap, with the cathode and protecting the tube in case the neutralizing condenser 22 breaks down, under which condition the voltage of the anode circuit from source 19 may be applied to the grid of the tube depending upon the external circuit and the position of blocking condenser 15 if used. The mid-tapiconnection with the cathode also s'erves'as an additional means for stabilizing tlievoltage'at afixed point on the reactor 21 or between the transformer windings. In the present'example the cathode lead is grounded as'in'dicated'at 24. I

' The action of this circuit is such that neutra'lizing voltage supplied through the neutralizing condenser 22-is reversed due to the transformer action and "appears on the grid of'the; tube in reverse phase to that voltage which is fed directly through the tube capacity, with the result that neutralization is accomplished. 4 Y "This neutr alizingmeans is easily applied to the coupling tube and serves to neutralize the coupled circuits regardless of the length ofthe' connections thereto, and since it may be applied directly to the tube at its terminals or substantially at its terminals, no additional circuit leadsbetween the impedances and the tubes are involved. For attachment to the circuits -of tube, the device is provided with an an'ode't'e'rminal 25, a cathode terminal 26 and a control electrode terminal 27.

circuit with the result that there is no high 7 frequency loss because of tube capacity.

The neutralizing means of the present invention has been successfully applied to tuned high frequency input and output .ClI'".

cuits coupled by a three element tube sub 'stantially as shown, when leads connecting the tuning elements of the circuits and the tube were several feet in length, thus clearly demonstrating its effectiveness under such unusual conditions in a high frequency circuit. Since the neutralizing means is applied directly to the tube, it serves to neutralize the elfect of the distributed capacity of the long leads without introducing similar leads in the neutralizing circuit as would be the case with known neutralizing systems.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination with an electric discharge device having an anode, a cathode and a control electrode, of an input circuit connected between said control electrode and said cathode, an output circuit connected between said anode and said cathode a source of anode potential connected in said circuit, and a neutralizing device including an inductance connected at one end with the control electrode and at the other endwith the anode, a neutralizing condenser interposed in circuit with said inductance and its connection with said anode, and a tap on said inductance connectedwith the cathode.

2. The combination with an electric discharge device having an anode, a cathode and a control electrode, of an input circuit connected between said control electrode and said cathode, an output circuit including a source of anode potential connected between said anode and said cathode, and a neutralizing device including a winding connected in shunt to the output circuit and said'source of potential in series, a neutralizing condenser in circuit with said winding and a second winding connected in'shunt to the input circuit, said windings being electro-magnetically close coupled in opposing phase relation.

3. The combination with an electric discharge amplifier device having a control electrode, a cathode and an anode, of a device for neutralizing the inter-electrode capacity of the amplifier device in connection with input and output circuits having relatively long connecting leads with said electrodes, said means'being adapted to be 1110- '1 plied directly to the amplifier device and including an anode terminal, a control electrode terminal, and a cathode terminal for connection with the electrodes of said amplifier device, an inductance winding connected between said anode and control electrode terminals, a neutralizing condenser connected between said winding and the anode terminal, and a tap on said winding connected with said cathode terminal.

In witness whereof, I have hereunto set my hand this 4th day of June, 1929.

' ANDREW D. RING. 

